EFFECT OF CHRONIC EXPOSURE TO GASEOUS AMMONIA ON THE NASAL TURBINATESOF GNOTOBIOTIC PIGS

Pigs reared in and stock persons working in intensive production syste ms are continuously exposed to ammonia released by microbial degradati on of animal excrement. Experimental studies have shown that exposure to this gas, at concentrations comparable to those encountered in buil dings used for the intensive rearing of swine, increases the severity of the clinical disease progressive atrophic rhinitis in pigs by facil itating colonization of the upper respiratory tract by toxigenic Paste urella multocida. During the course of these studies it was observed t hat mild turbinate atrophy also occurred in pigs from control groups e xposed to ammonia but maintained free from P. multocida and Bordetella bronchiseptica. To determine whether exposure to ammonia is detriment al to the normal anatomical development of the mammalian nasal cavity, a study was conducted using gnotobiotic piglets. Twenty-one gnotobiot ic piglets were derived from two sows by hysterectomy. Each litter was split into two groups, and the four groups were accommodated separate ly in sterile positive-pressure isolators supplied with high-efficienc y particulate air (HEPA) filtered air. From 1wk of age onward the air in the isolators housing one of the groups from each litter was modifi ed by the addition of ammonia at a concentration of 9.1 and 15.7 ppm. The air supply to the isolators housing the littermate groups was not modified. At 6 wk of age all the pigs were euthanatized. The effect of ammonia exposure on the morphology of the nasal cavity of the pig was assessed by image analysis of a cross section of the pig's snout. Pig s exposed to ammonia were found to have a mild but statistically signi ficant level of turbinate atrophy when compared to nonexposed litterma tes. Histological examination revealed that prolonged ammonia exposure evoked changes to the mucous membranes lining the nasal cavity, chara cterized by epithelial hyperplasia with micro-abscess formation, goble t-cell hypoplasia, and inflammatory cell infiltration. Mild degenerati ve changes within the bony core of the ventral turbinate were also app arent, with a decline in the population of osteoblasts and simultaneou s osteoclast proliferation. Group analysis revealed a correlation betw een the severity of turbinate atrophy and the increase in the number o f osteoclasts per unit area of bony core (p <. 05). These findings cou ld explain why mild turbinate atrophy is seen on some pig units deemed free from pathogenic bacteria associated with the clinical disease at rophic rhinitis.